The invention relates to the treatment of Semiconductor-On-Insulator (SeOI) structures for electronics or optoelectronics. Such SeOI structures comprise successively a semiconductor layer made of a semiconductor material (or bulk substrate), an oxide layer made of an oxide of the semiconductor material, and a bulk substrate. It is to be understood that the terms “electronic(s)” and “optoelectronic(s)” relate to any microelectronic, nanoelectronic, optomicroelectronic, optonanoelectronic, components technology made on or in the semiconductor layer.
The invention relates also to the manufacturing of these structures. Such structures are typically manufactured by using a wafer bonding technique, comprising the following steps:
providing a wafer with the semiconductor layer thereon;
providing a bulk substrate;
forming a dielectric layer on the semiconductor layer and/or on the bulk structure;
bonding the wafer with the bulk substrate, such that the dielectric layer is at the bonding interface between the semiconductor layer and the substrate;
reducing the wafer for only keeping the semiconductor layer bonded to the substrate via the dielectric layer, forming thus the SeOI structure; and
heat treating this structure in an atmosphere for reinforcing the bonding links.
In these structures, the dielectric layer is typically an oxide layer and/or a nitride layer. Even though nitride materials have a better resistance to high temperatures than oxide materials, oxide layers are often preferred to nitride layers for their better adhesive and dielectric properties, and also for the electrical quality provided by their interface. After bonding, if the dielectric is an oxide material, the dielectric layer is then a buried layer at the bonding interface, the so-called Buried OXide or BOX layer.
SeOI structures are applied for the manufacturing of electronic or optoelectronic components in the semiconductor layer. The buried dielectric layer allows the semiconductor layer to be electrically insulated from the bulk substrate. The performance of the components is then increased. Furthermore, due to a continuous progress in the field of semiconductors, the components need to be more and more miniaturized and to have lower power consumption and higher speed.
Thus, there is a need for reducing the thickness of both the semiconductor layer and the dielectric layer, while improving the uniformity of their respective thickness. But there are difficulties in manufacturing such thin layers. In particular, during heat treatment, some water and/or contamination particles, trapped during the bonding step at the interface between the two elements to be bonded, can cause internal pressure during heat treatment with a bad interface quality as a result.
If the semiconductor layer of the structure is sufficiently thick (typically more than 5 micrometers), water is absorbed by it, and partly rejected in the atmosphere. Drawbacks due to the presence of these molecules are thus avoided. Also, if the buried dielectric layer is thick enough (typically more than 200 angstroms for a BOX layer), these drawbacks can be also avoided.
Accordingly, it is necessary to have the buried dielectric layer or semiconductor layer that is thicker than their respective thickness limits for avoiding these problems. It is not possible to manufacture a SeOI structure with a semiconductor layer and a dielectric layer respectively thinner than these thickness limits, however, without risking deformation of the semiconductor layer or generating bubbles due to the presence of water. Accordingly, the quality of such a modified thickness semiconductor layer would not be acceptable for the next industrial process to implement.
US patent application 2005/0227444 and European patent application EP 1,583,143 attempt to solve these problems by proposing to manufacture a SOI structure with a thin silicon layer and a thin BOX layer (for “Silicon-On-Insulator” structure) by firstly operating a wafer bonding via a bonding oxide layer sufficiently thick for absorbing the interfacial molecules like for example water and/or hydrogen molecules, and then by reducing the thickness of the BOX layer by heat treating the SOI structure in a Argon or Hydrogen atmosphere. Indeed, oxygen of the BOX layer diffuses through the Si top layer to the surface of the SOI structure. However, this reducing in thickness of the BOX layer can decrease the dielectric quality of the BOX layer and the electrical properties at the interface with the Si top layer. Additionally, the final BOX layer lacks homogeneity in thickness and presents some surface roughness that causes bonding difficulties.
Thus, there remains a need for addressing these problems in a way that does not detract from the other desirable properties of the structure.